Field of the Invention
The invention relates to a leather, on the buffed surface of which a finish has been provided, where the finish has an outer layer with a particular surface effect, which has been prefabricated on a hot substrate having a structure corresponding to this surface effect, and comprises a solidified, polyurethane-containing dispersion, and also has an inner layer which has been bonded to the buffed surface of the leather and likewise comprises a solidified, polyurethane-containing dispersion. For the purposes of the invention, th4e term "leather" means either natural leather, the buffed grain side of which has been provided with a finish, or else split leather whose buffed surface has been provided with a finish.
German Patent 32 29 150 discloses a finished split leather in which the finish is composed of two layers. Here, an aqueous polyurethane dispersion is applied to a substrate heated to a temperature of from 70 to 185.degree. C. and solidifies on the substrate to give a film. The film is thereupon bonded, using pressure and suction, to the split-leather surface by a polyurethane dispersion comprising hollow microspheres. This method cannot produce thin finishes.
European Patent 105 046 describes a finished split leather in which the finish is likewise composed of two layers. An inner layer adjacent to the split leather has a thickness of from 0.12 to 0.45 mm, i.e. a substantial thickness. The properties of the leather are thereby adversely affected.
German published patent application 195 10 242 has disclosed a full-grain natural leather whose grain side has been provided with a finish which is applied to shaped pieces cut out from the natural leather. The finish there is composed of two layers formed by solidifying an aqueous, polyurethane-containing polymer dispersion. That finish has a thickness of up to 0.13 mm.
German published patent application 195 10 240 discloses the application of a finish with a varied surface effect and a thickness of up to 0.15 mm to a leather support having a specified margin.
German Utility Model 298 12 075.5 describes a full-grain natural leather provided with a finish and having a specified margin for producing automotive parts and composed of three layers each comprising a polyurethane dispersion. The outermost layer here has a particular surface effect and is prefabricated on a hot substrate having a corresponding structure, and its Shore hardness is greater than those of the intermediate and inner layers. This is claimed to ensure that the leather has the properties required for producing automotive parts.
German published patent application 37 20 776 discloses a leather material provided with a finish which is composed of a relatively thick leveling layer bonded to the leather and, applied thereto, a top layer which forms the visible surface and may be composed of two sublayers arranged one on top of the other, where there may be provision of a primer between the individual layers to improve adhesion, if desired. The leveling layer here is applied to the leather surface as a leveling substrate in the form of granules of leveling material. A finish of this type has substantial thickness, resulting in loss of leather properties.
In prior art leathers provided with a finish, the outer layer with a visible surface is bonded to the split leather by applying the material forming the inner layer in the wet state either to the leather surface or to the solidified outer layer, then laminating while supplying heat, whereupon some of the wet material penetrates into the leather and levels any uneven areas in the leather surface. It is therefore necessary to apply an appropriately large amount of the material forming the inner layer in order to ensure leveling of the uneven areas in the leather surface and reliable bonding, and this entails the thicknesses mentioned. The result is that known finished leathers have only low water-vapor permeability and water-vapor coefficients and therefore do not fulfill the requirements frequently placed upon leather.